1. Field of the Invention
The present invention relates generally to a high-speed wireless packet data communication system, and in particular, to an apparatus and method for supporting automatic repeat request.
2. Description of the Related Art
Wireless communication systems have been developed to enable users to continue smooth communication while travelling. The development of a wireless communication technology has given impetus to research in technology for transmitting large quantities of data to users.
Wideband Code Division Multiple Access (W-CDMA) wireless communication system a typical CDMA2000 1× system, were designed to support only voice service and relatively low-speed packet data service. However, with the development of communication technology and at the request of users, research has been carried out in wireless communication systems supporting a high-speed packet data service. Among others, one example is an IS-2000 1×EV-DV (Evolution in Data and Voice) system, which is the new CDMA standard developed by 3GPP2 (3rd Generation Partnership Project 2). This is considered as the preferred system for supporting not only a voice service, but also high-speed packet data service. In order to realize a system capable of supporting both high-speed packet data service as well as voice service, it is necessary to design both a base station (BS) and mobile station (MS) capable of handling high-speed wireless packet data.
In a wireless channel environment characterized in that variation in channel conditions are considerable and traffic channels for different types of services coexist, automatic repeat request (hereinafter referred to as “ARQ”) is used to increase transmission efficiency, or transmission throughput, for high-speed data transmission. According to ARQ protocols, a receiver requests retransmission when an error has occurred in received data, and a transmitter retransmits the data in response to the request so that the receiver can obtain reception quality over a predetermined level.
In a typical wireless communication system, ARQ could not be considered for a voice call service, since the voice call service is requested real-time processing. Thus, ARQ was restrictively supported in an upper layer for a circuit-based data service only. As a proposal for increasing transmission throughput, a proposal has been made for supporting ARQ in a physical layer rather than in the upper layer, and this proposal is discussed as a part of the standard for a high-speed wireless packet data communication system (e.g., 1×EV-DV system) that is currently being developed.
In a currently discussed system, a receiver corrects an error existing in received data within the limit of its error correction capability, but sends a retransmission request message to a transmitter when it cannot correct the error: this technology is called hybrid ARQ (hereinafter referred to as “H-ARQ”). Since commercialization of a high-speed data transmission service will soon be available, analysis and research has been conducted on a technology for efficiently applying, in an actual system, new H-ARQ where a variable coding rate error correction code is used rather than existing hybrid H-ARQ where a fixed coding rate error correction code is used. Furthermore, at least one study has been made of a method for applying, to the system, high level modulation e.g., 8-ary phase shift keying (8PSK), 16-ary quadrature amplitude modulation (16QAM), binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK), for a high-speed transmission channel structure.
The new CDMA standard, the IS-2000 1×EV-DV system adopts a coding scheme using quasi-complementary turbo codes (QCTC). The QCTC supports the variable coding rate for H-ARQ on high-speed data, and secures improvement of soft-combining performance by H-ARQ. In the 1×EV-DVsystem, transmission and reception of packet data is performed by H-ARQ or fast H-ARQ of a physical layer.
When implementing H-ARQ, many factors should be considered in terms of system complexity, such as buffer size and signaling load of a transmitter and a receiver, in addition to the transmission throughput. Accordingly, there have been demands for a control algorithm for more efficiently managing H-ARQ for improving system efficiency and service quality in a high-speed wireless packet data communication system.